On the coupling between membrane bending and stretching in lipid vesicles

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Lipid vesicle formation from lamellar phases incurs significant bending energy costs.
• Membrane bending rigidity is inversely related to bilayer thickness.

Purpose of the Study:

• To model the coupling between bending and stretching in lipid bilayers.
• To analyze the impact of this coupling on vesicle bending energy and thermal fluctuations.
• To investigate the implications for vesicle size limitations and protein adsorption.

Main Methods:

• Development of a simple theoretical model for bilayer bending-stretching coupling.
• Analysis of the model's predictions for spherical lipid vesicles.
• Examination of the relationship between bilayer thinning, free energy, and vesicle stability.

Main Results:

• Bilayer thinning becomes significant in small vesicles, reducing bending energy.
• Thermally excited bending modes lead to a substantial decrease in free energy due to thinning.
• A critical thinning point exists, beyond which vesicles become unstable.

Conclusions:

• Bilayer thinning is a key mechanism reducing the energetic cost of small vesicle formation.
• This effect explains the experimentally observed lower limit for vesicle sizes.
• The curvature-dependent thinning may provide a generic mechanism for protein-membrane interactions.